1. Field of the Invention
This invention is directed to a process of zinc coating fasteners, such as screws and nuts.
2. Prior Art
One known process of zinc coating is the heat-coating process wherein the articles to be coated are dipped into a bath of molten zinc. This process produces a heavy zinc coat thickness, a rather even total zinc distribution, also on complicated articles, and a good resistance to corrosion. However, this process provides a bad surface finish and there is a risk of local zinc accumulations. Such local zinc accumulations may cause problems at the application of the fasteners and hot-coated fasteners can, for this reason, seldom be used in automatic applicators. Furthermore, the possibility to protect the hot-coated layers against self-corrosion (so called white-blisters) by chromating is limited.
Another known process of zinc coating is the electrocoating process. This process produces a good surface finish, and the application or assembling properties with smaller zinc coat thicknesses present are good; also, this process permits different kinds of chromating. However, with greater zinc coat thicknesses, the electrocoating process gives rise to an uneven zinc distribution due to a so called point-effect; further, the resistance to corrosion is comparatively low, and there exists a risk for hydrogen absorption.